Haptic system with increased lra bandwidth

ABSTRACT

A method of generating a haptic effect on a linear resonance actuator (“LRA”) having a resonant frequency includes receiving a haptic effect signal for the haptic effect, where the haptic effect comprises a desired frequency that is off-resonant from the LRA. The method further includes generating a first sine wave at the desired frequency and generating a second sine wave at or near the resonant frequency. The method further includes combining the first sine wave and the second sine wave to generate a drive signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/105,481, filed on Dec. 12, 2013, currently pending, which claimspriority of U.S. Provisional Patent Application Ser. No. 61/736,912,filed on Dec. 13, 2012, and U.S. Provisional Patent Application Ser. No.61/790,190, filed on Mar. 15, 2013. The contents of each of theforegoing applications is hereby incorporated by reference.

FIELD

One embodiment is directed generally to a system that generates hapticeffects, and in particular to a system that generates haptic effectsusing a linear resonance actuator.

BACKGROUND INFORMATION

Portable/mobile electronic devices, such as mobile phones, smartphones,camera phones, cameras, personal digital assistants (“PDA”s), etc.,typically include output mechanisms to alert the user of certain eventsthat occur with respect to the devices. For example, a cell phonenormally includes a speaker for audibly notifying the user of anincoming telephone call event. The audible signal may include specificringtones, musical ditties, sound effects, etc. In addition, cell phonesmay include display screens that can be used to visually notify theusers of incoming phone calls.

In some mobile devices, kinesthetic feedback (such as active andresistive force feedback) and/or tactile feedback (such as vibration,texture, and heat) is also provided to the user, more generally knowncollectively as “haptic feedback” or “haptic effects”. Haptic feedbackcan provide cues that enhance and simplify the user interface.Specifically, vibration effects, or vibrotactile haptic effects, may beuseful in providing cues to users of electronic devices to alert theuser to specific events, or provide realistic feedback to create greatersensory immersion within a simulated or virtual environment. In order togenerate vibration effects, many devices utilize some type ofactuator/motor or haptic output device. Known actuators used for thispurpose include a linear resonance actuator.

SUMMARY

One embodiment is a method of generating a haptic effect on a linearresonance actuator (“LRA”) having a resonant frequency. The methodincludes receiving a haptic effect signal for the haptic effect, wherethe haptic effect comprises a desired frequency that is off-resonantfrom the LRA. The method further includes generating a first sine waveat the desired frequency and generating a second sine wave at or nearthe resonant frequency. The method further includes combining the firstsine wave and the second sine wave to generate a drive signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a haptically-enabled system in accordancewith one embodiment of the present invention.

FIG. 2 illustrates the handling of the frequency parameter of a hapticeffect in accordance with one embodiment of the present invention.

FIG. 3 illustrates a complex waveform using a carrier wave in accordancewith one embodiment.

FIG. 4 illustrates a complex waveform using a scaled product inaccordance with one embodiment.

FIGS. 5a-5d illustrate various waveforms of the scaled product inaccordance with one embodiment.

FIG. 6 is a flow diagram of the functionality of the system of FIG. 1when generating haptic effects using an LRA in accordance with oneembodiment.

FIG. 7 illustrates an example graph of an LRA generating haptic effectsprimarily at resonant frequency, and a graph of an LRA generating hapticeffects with an increased range/bandwidth in accordance with embodimentsof the present invention.

DETAILED DESCRIPTION

One embodiment is a system that generates haptic effects using a linearresonance actuator (“LRA”). Embodiments combine multiple signals inorder to drive the LRA at off-resonant frequencies to increase thebandwidth of the LRA.

One type of LRA may use a movable mass, permanent magnet, voice coil andspring to generate vibrations. The voice coil produces a magnetic fieldwhich interacts with the permanent magnet, causing it to move, whichcompresses or stretches the spring to which it is attached. The drivesignal needs to alternate the direction of current (i.e., an alternatingcurrent (“AC”) signal) and generate the magnetic field to make thepermanent magnet oscillate back and forth with the spring. The movingmass is attached to the magnet, and the moving of the mass back andforth generates the vibrations. Another type of LRA may include two ormore layers of piezo-electric ceramics with a mass attached so that whenthe piezo bends, the mass moves in a linear/oscillating fashion.Additional types of LRAs that include a vibrating motor that is drivenwith an oscillating signal can also be used with embodiments disclosedherein.

AC drive signals can have a frequency and an amplitude. The higher theamplitude the greater the vibration output for a given frequency.However, the frequency of the drive signal can be an important factor.An LRA has a resonant frequency which the input signal should operateat, in order to maximize the vibration generated. Vibration performancedrops off significantly when the input signal frequency is moved too farfrom the resonant frequency. Therefore, most haptic devices apply adrive signal at the resonant frequency of the LRA when generating hapticeffects. Most LRAs used to generate haptic effects have a resonantfrequency within the 150-200 Hz range.

In contrast with known haptic systems that use LRAs, the type of hapticeffects generated by embodiments of the present invention require anincreased range/bandwidth of an LRA, outside of its resonant frequency,to be effective. Specifically, FIG. 1 is a block diagram of ahaptically-enabled system 10 in accordance with one embodiment of thepresent invention. System 10 includes a touch sensitive surface 11 orother type of user interface mounted within a housing 15. System 10further includes a pen/stylus 13 that is in communication with the restof system 10 using a wireless (e.g., Bluetooth) or wired communicationlink.

Internal to system 10 is a haptic feedback system that generatesvibrations 30, 31 on stylus 13, as well as optionally on other areas ofsystem 10, such as on touch surface 11 or housing 15. The hapticfeedback system includes a processor or controller 12. Coupled toprocessor 12 is a memory 20 and an actuator drive circuit 16, which iscoupled to an LRA 18. Processor 12 may be any type of general purposeprocessor, or could be a processor specifically designed to providehaptic effects, such as an application-specific integrated circuit(“ASIC”). Processor 12 may be the same processor that operates theentire system 10, or may be a separate processor. Processor 12 candecide what haptic effects are to be played and the order in which theeffects are played based in part on high level parameters. In general,the high level parameters that define a particular haptic effect includemagnitude, frequency and duration. Low level parameters such asstreaming motor commands could also be used to determine a particularhaptic effect. A haptic effect may be considered “dynamic” if itincludes some variation of these parameters when the haptic effect isgenerated or a variation of these parameters based on a user'sinteraction.

Processor 12 outputs the control signals to actuator drive circuit 16,which includes electronic components and circuitry used to supply LRA 18with the required electrical current and voltage (i.e., “motor signals”)to cause the desired haptic effects. System 10 may include more than oneLRA 18, or other type of actuator, and each actuator may include aseparate drive circuit 16, all coupled to a common processor 12.

Memory device 20 can be any type of storage device or computer-readablemedium, such as random access memory (“RAM”) or read-only memory(“ROM”). Memory 20 stores instructions executed by processor 12. Amongthe instructions, memory 20 includes a haptic effects module 22 whichare instructions that, when executed by processor 12, generate drivesignals for LRA 18 that increase the output bandwidth of LRA 18, asdisclosed in more detail below. Memory 20 may also be located internalto processor 12, or may be any combination of internal and externalmemory.

Touch surface 11 recognizes touches, and may also recognize the positionand magnitude of touches on the surface. The data corresponding to thetouches is sent to processor 12, or another processor within system 10,and processor 12 interprets the touches and in response can generatehaptic effect signals. Touch surface 11 may sense touches using anysensing technology, including capacitive sensing, resistive sensing,surface acoustic wave sensing, pressure sensing, optical sensing, etc.Touch surface 11 may sense multi-touch contacts and may be capable ofdistinguishing multiple touches that occur at the same time. Touchsurface 11 may be a touchscreen that generates and displays images forthe user to interact with, such as keys, dials, etc., or may be atouchpad with minimal or no images.

System 10 may be a handheld device, such a cellular telephone, personaldigital assistant (“PDA”), smartphone, computer tablet/pad, gamingconsole, etc., or may be any other type of device that includes a hapticeffect system that includes one or more LRAs. System 10 may also be awearable device (e.g., a bracelet, armband, glove, jacket, vest, pair ofglasses, shoes, belt, etc.) that includes one or more LRAs that generatehaptic effects. The user interface may be a touch sensitive surface, orcan be any other type of user interface such as a mouse, touchpad,mini-joystick, scroll wheel, trackball, game pads or game controllers,etc.

In one embodiment, LRA 18 and drive circuit 16 are located within stylus13, and generate haptic effects directly on stylus 13. In thisembodiment, the remaining elements of the haptic effect system arelocated within housing 15, and are in communication with stylus 13. Asdiscussed above, system 10 requires LRA 18 to have a wider frequencyresponse range than standard LRAs because it has a need to generate awide variety of haptic effects to be designed off-resonance. Forexample, one embodiment generates haptic effects on stylus 13 tosimulate a texture when used by a user to “draw” on screen 11. Furthergenerated haptic effects by LRA 18 can cause stylus 13 to simulate a penor pencil using different off-resonance haptic signals (i.e., stylus 13can feel to a user like a pencil or a pen, depending on which hapticeffect is generated by LRA 18). These types of haptic effects mayfurther require the independent variation of the frequency and strengthof the vibration.

Known haptic effect systems (e.g., the “Touchsense 3000” from ImmersionCorp.) that use an LRA typically use a controller to communicate thehaptic drive signal using a pulse-width modulation (“PWM”) signal (i.e.,a rectangular pulse wave whose pulse width is modulated). These knownsystems require an AC drive signal whose frequency generally correspondsto the actuator's resonant frequency (typically 175 Hz). In contrast,one embodiment allows for the independent control of frequency andstrength on the LRA to increase the bandwidth of the LRA.

FIG. 2 illustrates the handling of the frequency parameter of a hapticeffect in accordance with one embodiment of the present invention. Inthe example of FIG. 2, the haptic effect is ultimately rendered orplayed by a “TS5000 Player” from Immersion Corp. and will be interpretedin different ways based on its frequency characteristics.

Specifically, for low frequencies (e.g., less than 20 Hz) such as inputeffect 202, the frequency and wave shape will be interpreted as anenvelope. For example, if the effect is a sine wave, the strength of theeffect will rise and fall following the shape of the sine wave. Theoutput effect 208 will be at the resonant frequency of the LRA and willbe modulated by the input effect 202. Depending on actuatorcapabilities, this pulsing effect can only be done if the designedfrequency is around 20 Hz or lower in one embodiment. The exactfrequency for this pulsing range depends on the LRA's resonant frequencyand the rise time (or the time it takes the actuator to reach nominalacceleration).

For high frequencies (e.g., greater than 150 Hz) such as input effect210, the frequency parameter will be passed through to a ServiceProvider Interface (“SPI”) 213 or other interface unit. SPI 213 in oneembodiment is responsible for sending the frequency and strength valuesto stylus 13 (over Bluetooth or other medium), and scales the effectstrength to match the envelope. This technique is effective for a rangeof frequencies near the resonance frequency of the LRA (e.g.,approximately 150-250 Hz).

In contrast to the “low” and “high” frequency haptic effects describedabove, for “mid-range” frequency haptic effects (e.g., 20-150 Hz),embodiments transition between the above modes. The frequency rangedepends upon the actuator used and could be lower than a typical orcommon medium frequency range for an LRA. For example, the lower end ofthe middle range could be less than or equal to 2 Hz and a high end ofthe middle range could be equal to or greater than 200 Hz. Embodimentsimplement one or more of the below techniques for transitioning betweenthe high and low frequency in order to generated increased LRA bandwidthhaptic effects.

Transition Point

In one embodiment, a single point in the critical range (i.e.,“mid-range” frequencies, for example, 20-150 Hz) is selected. Anydesired frequency below that point is rendered by enveloping a signal atresonant frequency with a sine wave at the desired frequency. Anydesired frequency above this point is used to directly drive theactuator. However, the transition from one drive mode to the other maybe abrupt and the strength of the vibration may be very weak near thetransition point. The greater the disparity between the wavelength ofthe signal at resonance and rise time plus fall time, the less effectivethe single transition point becomes.

The transition point may be determined algorithmically by measuringacceleration using an accelerometer mounted to the device, such as beingmounted on LRA 18. The drive signal for the test is made up of a sine orsquare wave at the device's resonant frequency multiplied by a sine wavethat varies in frequency from low to high (frequency sweep), spanningthe critical range. The acceleration will rise and fall with theenvelope wave and the peak acceleration during each period decreases asthe envelope frequency increases. Additionally, a sine wave frequencysweep (without the resonant component) is played, generating a secondacceleration trace that generally increases in strength as the frequencyincreases until it reaches the resonant frequency of the device. Thebest transition point for optimizing strength is where the graphs ofthese two accelerometer traces cross.

In another embodiment, the transition point may be determined manuallyby a user feeling these two frequency sweeps. It may be desirable tohave a lower or higher transition point based on personal preference orother factors.

Design Choice

In another embodiments, the transition point can be a design-timedecision, so that the haptic effect designer (using, e.g., the “HapticStudio” from Immersion Corp.) may choose which mode to use for theeffect. Embodiments may implement this decision by providing anadditional parameter to the definition of the effect, expanding existingparameters to include additional discrete values, or repurposing orredefining existing parameters.

Carrier Wave

Another embodiment uses the desired frequency of the haptic effect as acarrier wave added to the resonant frequency. In order to increase theuseable frequency range while maintaining the strength in thetransitional region, two complex waveforms may be used. FIG. 3illustrates a complex waveform 300 using a carrier wave in accordancewith one embodiment. Waveform 300 of FIG. 3 is the sum of two sinewaves, although the higher frequency wave can also be a square wave.Waveform 300 is defined as follows:

y=V _(desired) [A sin(2πf _(desired) t)+B sin(2πf _(resonant) t)]

where A+B=1, V_(desired) is the desired driving voltage of the actuator,and f_(resonant) is an integer multiple of f_(desired) that is as closeas possible to the true resonant frequency of the LRA in order to avoidphasing waveforms. One embodiment determines f_(resonant) by multiplyingthe desired frequency f_(desired) by an integer so that the result is asclose as possible to the true resonant frequency. For example, if theactual resonant frequency is 175 Hz and the desired is 55 Hz, a factorof 3 will result in a 165 Hz value for f_(resonant). A factor of 4 wouldresult in a 220 Hz value. 165 Hz is closer to the true resonantfrequency, so that is what would be used.

Scaled Product

In another embodiment, to smoothly transition between sine-envelopedpulsing and direct-drive modes, the enveloped signal can be added to asine wave at or near resonance to produce a composite of both drivesignals as follows:

y=V _(desired) [A sin(2πf _(desired) t)sin(2πf _(resonant) t)+B sin(2πf_(desired) t)]

where A+B=1. A and B are scaled inversely over the transitional rangesuch that the enveloped resonant signal is dominant at the low end ofthe range, and the direct-drive signal is dominant near the high end ofthe range. V_(desired) is the desired driving voltage of the actuator,and f_(resonant) is a multiple of f_(desired) that is as close aspossible to the true resonant frequency of the actuator in order toavoid phasing waveforms. FIG. 4 illustrates a complex waveform 400 usinga scaled product in accordance with a embodiment.

FIGS. 5a-5d illustrate various waveforms of the scaled product inaccordance with one embodiment. FIG. 5a illustrates a resonant frequencywaveform 501 and a slow enveloped waveform 502 to which it will bemultiplied by in accordance with one embodiment. FIG. 5b illustrates ascaled envelope waveform 503 of FIG. 5a in accordance with oneembodiment. FIG. 5c illustrates a scaled direct drive waveform 504 inaccordance with one embodiment. FIG. 5d illustrates a scaled compositewaveform 505 formed from the scaled envelope waveform 503 of FIG. 5badded to the scaled direct drive waveform 504 of FIG. 5c in accordancewith one embodiment.

In all embodiments described above, driving an LRA off-resonance willresult in a reduction of strength in the haptic effect. Therefore, someembodiments boost the off-resonance drive signals to achieve a flatterresponse curve (i.e., the graph of acceleration measured byaccelerometer vs. drive frequency). Embodiments can boost the signalusing one or more of the following, in addition to other known methods:

-   -   1. Applying a gain to each sine wave that contributes to the        signal independently;    -   2. Multiplying the computed composite wave by a scale factor        based on the frequencies present; and    -   3. Multiplying the computed composite wave by a predefined scale        factor and applying one or more filters (e.g., notch, high-pass,        low-pass, etc.) to attenuate the strength at the resonant        frequency.

FIG. 6 is a flow diagram of the functionality of system 10 of FIG. 1when generating haptic effects using an LRA in accordance with oneembodiment. In one embodiment, the functionality of the flow diagram ofFIG. 6 is implemented by software stored in memory or other computerreadable or tangible medium, and executed by a processor. In otherembodiments, the functionality may be performed by hardware (e.g.,through the use of an application specific integrated circuit (“ASIC”),a programmable gate array (“PGA”), a field programmable gate array(“FPGA”), etc.), or any combination of hardware and software.

At 602, the haptic effect signal is received. The haptic effect signalhas a frequency (i.e., the desired frequency or “f_(desired)”) that isan off-resonant frequency of the LRA (i.e., not at the LRA's resonantfrequency) that will generate the haptic effect.

At 604, a sine wave at the desired frequency is generated.

At 606, a sine wave at or near the resonant frequency of the LRA isgenerated. In one embodiment, the sine wave frequency is the frequencythat is an integer multiple of the off-resonant frequency but is asclose to the resonant frequency as possible (“f_(resonant)”).

At 608, the sine waves from 604 and 606 are combined and multiplied bythe maximum rated driving voltage of the LRA to generate the resultanthaptic effect signal. In one embodiment, the sine waves are combined asfollows:

y=V _(desired) [A sin(2πf _(desired) t)+B sin(2πf _(resonant) t)]

In another embodiment., the sine waves are combined as follows:

y=V _(desired) [A sin(2πf _(desired) t)sin(2πf _(resonant) t)+B sin(2πf_(desired) t)]

The calculations are between 0 and 1, so this resulting scalar would bemultiplied by the maximum drive voltage the LRA can handle. In oneembodiment, the calculations use integer math in the range of −127 . . .127 rather than floating point from 0 . . . 1.

As disclosed, embodiments generate haptic effects that include anoff-resonant frequency component. In generating the haptic effect, thebandwidth of the LRA that generates the haptic effect is expanded sothat it can render the haptic effects. FIG. 7 illustrates an examplegraph 702 of an LRA generating haptic effects primarily at resonantfrequency, and a graph 704 of an LRA generating haptic effects with anincreased range/bandwidth in accordance with embodiments of the presentinvention.

Several embodiments are specifically illustrated and/or describedherein. However, it will be appreciated that modifications andvariations of the disclosed embodiments are covered by the aboveteachings and within the purview of the appended claims withoutdeparting from the spirit and intended scope of the invention. Forexample, although some embodiments use an LRA, any system with anactuator device that experiences a sharp fall-off in performance atoff-resonance frequencies when generating haptic effects can useembodiments of the present invention.

What is claimed is:
 1. A method of generating a vibratory haptic effectby a linear resonance actuator (LRA) having a resonant frequency, themethod comprising: receiving an input haptic effect signal comprising adesired input frequency; determining whether the desired input frequencyis below or above a transition point frequency; when the desired inputfrequency is below the transition point frequency, generating a firstoutput haptic effect signal by enveloping the input haptic effect signalat the resonant frequency with a sine wave at the desired inputfrequency; and applying the first output haptic effect signal to the LRAto generate the vibratory haptic effect.
 2. The method of claim 1,further comprising: when the input frequency is above the transitionpoint frequency, using the input haptic effect signal as a second outputhaptic effect signal; applying the second output haptic effect signal tothe LRA to generate the vibratory haptic effect.
 3. The method of claim1, further comprising: determining the transition point frequency usingan input signal generated by an accelerometer mounted on the LRA ormounted on a device housing the LRA.
 4. The method of claim 1, whereinthe first output haptic effect signal comprises a pulse-width modulation(PWM) signal at the resonant frequency.
 5. The method of claim 2,wherein the second output haptic effect signal comprises a pulse-widthmodulation (PWM) signal at the desired input frequency.
 6. The method ofclaim 5, wherein the second output haptic effect signal is scaled tomatch an envelope.
 7. The method of claim 1, wherein when the desiredinput frequency is below the transition point frequency, the desiredinput frequency is an off-resonance frequency.
 8. The method of claim 1,wherein the first output haptic effect signal comprises off-resonancedrive signals, further comprising boosting the off-resonance drivesignals before applying.
 9. The method of claim 1, wherein the LRA ishoused in one of a stylus, a game controller, or a wearable device. 10.A haptic effect system comprising: a linear resonance actuator (LRA)having a resonant frequency; an actuator drive circuit coupled to theLRA; a controller coupled to the actuator drive circuit, wherein thecontroller receives an input haptic effect signal comprising a desiredinput frequency; the controller adapted to determine whether the desiredinput frequency is below or above a transition point frequency, and whenthe desired input frequency is below the transition point frequency,generate a first output haptic effect signal by enveloping the inputhaptic effect signal at the resonant frequency with a sine wave at thedesired input frequency, and transmit the first output haptic effectsignal to the actuator drive circuit; the actuator drive circuit appliesthe first output haptic effect signal to the LRA, causing the LRA togenerate a vibratory haptic effect.
 11. The haptic effect system ofclaim 10, the controller further adapted to, when the input frequency isabove the transition point frequency, use the input haptic effect signalas a second output haptic effect signal; the actuator drive circuitapplying the second output haptic effect signal to the LRA to generatethe vibratory haptic effect.
 12. The haptic effect system of claim 10,further comprising: an accelerometer mounted on the LRA or mounted onthe system housing the LRA; the controller further adapted to determinethe transition point frequency using an input signal generated by theaccelerometer.
 13. The haptic effect system of claim 10, wherein thefirst output haptic effect signal comprises a pulse-width modulation(PWM) signal at the resonant frequency.
 14. The haptic effect system ofclaim 11, wherein the second output haptic effect signal comprises apulse-width modulation (PWM) signal at the desired input frequency. 15.The haptic effect system of claim 14, wherein the second output hapticeffect signal is scaled to match an envelope.
 16. The haptic effectsystem of claim 10, wherein when the desired input frequency is belowthe transition point frequency, the desired input frequency is anoff-resonance frequency.
 17. The haptic effect system of claim 10,wherein the first output haptic effect signal comprises off-resonancedrive signals, the controller further adapted to boost the off-resonancedrive signals before applying.
 18. The haptic effect system of claim 10,wherein the LRA is housed in one of a stylus, a game controller, or awearable device.
 19. A non-transitory computer-readable medium havinginstructions stored thereon that, when executed by a processor, causethe processor to generate a vibratory haptic effect by a linearresonance actuator (LRA) having a resonant frequency, the processor:receiving an input haptic effect signal comprising a desired inputfrequency; determining whether the desired input frequency is below orabove a transition point frequency; when the desired input frequency isbelow the transition point frequency, generating a first output hapticeffect signal by enveloping the input haptic effect signal at theresonant frequency with a sine wave at the desired input frequency; andapplying the first output haptic effect signal to the LRA to generatethe vibratory haptic effect.
 20. The computer-readable medium of claim19, the processor: when the input frequency is above the transitionpoint frequency, using the input haptic effect signal as a second outputhaptic effect signal; applying the second output haptic effect signal tothe LRA to generate the vibratory haptic effect.